U.S. patent number 4,628,005 [Application Number 06/678,704] was granted by the patent office on 1986-12-09 for heat wave shielding lamination.
This patent grant is currently assigned to Kabushiki Kaisha Toyoto Chuo Kenkyusho. Invention is credited to Tadayoshi Ito, Taga Yasunori.
United States Patent |
4,628,005 |
Ito , et al. |
December 9, 1986 |
**Please see images for:
( Certificate of Correction ) ** |
Heat wave shielding lamination
Abstract
A heat wave shielding lamination having improved abrasion
resistance is composed of a visible light transparent substrate and
an overlying composite lamination in which layers of a visible
light transparent substance of a low refractive index and layers of
a visible light transparent substance of a high refractive index
are alternately arranged on each other, with the topmost layer
being a low-refractance layer, and interfacial layers of Al.sub.2
O.sub.3 which are much thinner than the high-refractance and
low-refractance layers are provided between the high-refractance
and low-refractance layers.
Inventors: |
Ito; Tadayoshi (Aichi,
JP), Yasunori; Taga (Aichi, JP) |
Assignee: |
Kabushiki Kaisha Toyoto Chuo
Kenkyusho (Aichi, JP)
|
Family
ID: |
16951696 |
Appl.
No.: |
06/678,704 |
Filed: |
December 6, 1984 |
Foreign Application Priority Data
|
|
|
|
|
Dec 9, 1983 [JP] |
|
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58-233224 |
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Current U.S.
Class: |
428/432; 428/469;
428/472; 428/698; 428/700; 428/701 |
Current CPC
Class: |
G02B
5/208 (20130101) |
Current International
Class: |
G02B
5/20 (20060101); G02B 001/10 () |
Field of
Search: |
;428/432,700,701,698,699
;427/34,250,255,469,471,472 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Swisher; Nancy A. B.
Attorney, Agent or Firm: Koda and Androlia
Claims
What is claimed is:
1. A heat wave shielding lamination having improved abrasion
resistance, without effecting its optical characteristics,
comprising: a visible light transparent substrate; and an overlying
composite lamination consisting of at least two layers of visible
light transparent substance of a low refractive index and at least
two layers of visible light transparent substance of a high
refractive index lying alternately on each other, with the topmost
layer being said low-refractive layer, and at least one interfacial
layer of Al.sub.2 O.sub.3 provided between said high-refractance
and low-refractance layers, said interfacial layer being much
thinner than said high-refractance and low-refractance layers with
the thickness of the interfacial layer being in the range of 5-20
nm said high-refractance layers being formed of a material selected
from TiO.sub.2, CeO.sub.2, ZnS, CdS and ZrO.sub.2, each of which
being thick enough to reflect infrared rays, and said
low-refractance layers being formed of a material selected from
SiO.sub.2, MgF.sub.2, LiF, CeF.sub.3 and CaF.sub.2, the top most
layer thereof being of a thickness which prevents reflection of
visible light and other layers thereof being thick enough to
reflect infrared rays.
2. A heat wave shielding lamination according to claim 1, wherein
said interfacial layer of Al.sub.2 O.sub.3 is provided between the
uppermost high-refractance and low-refractance layers.
3. A heat wave shielding lamination according to claim 1, wherein
said interfacial layer of Al.sub.2 O.sub.3 is provided at each
interface between said high-refractance and low-refractance
layers.
4. A heat wave shielding lamination according to claim 1, wherein
said visible light transparent substance is formed of glass or
plastic.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a heat wave shielding lamination, and
more particularly to an improved heat wave shielding lamination
comprising a plurality of thin layers laminated on the surface of a
visible light transparent substrate.
2. Description of the Prior Art
Progress is being made in the development and practical application
of heat wave shielding laminations consisting of thin layers of
visible light transmitting material of a high refractive index
alternating with those of a low refractive index formed on the
surface of a visible light transparent substrate of glass or
plastic. Because of their excellent transparency to visible light
and their outstanding heat wave reflection characteristics, such
heat wave shielding laminations are expected to be widely used on
the window glass of automobiles or of buildings and in a wide range
of other fields.
However, a drawback with the conventional heat wave shielding
laminations has been that they did not provide the
abrasion-resistance required for practical application, and because
of this efforts to apply conventional heat wave shielding
laminations have been extremely limited to such uses as heat
shields in electronic copying machines and other such applications
where the conditions of use are not so stringent. It has not been
possible to apply such laminations to the windows of automobiles or
of buildings owing to their lack of sufficient abrasion-resistance.
For the same reason it was not possible to apply such laminations
to plastic substrate materials.
Specifically, to use such heat wave shielding laminations for the
windows of automobiles, they are required to pass the Taber
abrasion test, one of the durability tests stipulated by JIS for
automobile window glass. Evaluation of the abrasion resistance is
on the basis of the haze value obtained after the test, and it is
laid down in the JIS standard that the amount of abrasion measured
thus must not exceed 2%.
However, in the actual testing of conventional heat wave shielding
laminations interlayer peeling occurred at the interface between
the high-refraction and low-refraction films, resulting in haze
values in excess of 2% and therefore precluding the use of such
laminations for the windows of automobiles.
Furthermore, in order to improve their abrasion-resistance
conventional heat wave shielding laminations, together with their
glass substrate, were subjected to heat treatment at high
temperatures of around 500.degree.-600.degree. C. or more. However,
such high-temperature heat treatment could not be applied to the
window glass of automobiles, to spectacle or camera lenses or to
substrates of plastic, and this formed an obstacle to the practical
utilization of heat wave shielding laminations.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide a heat
wave shielding lamination which has sufficient abrasion-resistance
without the need to resort to high-temperature heat treatment.
This object of the present invention is attained by providing a
heat wave shielding lamination comprising a visible light
transparent substrate and an overlying composite lamination in
which layers of visible light transparent substance of a low
refractive index and layers of visible light transparent substance
of a high refractive index are alternately on each other, and
interfacial layers of Al.sub.2 O.sub.3 which are much thinner than
the high-refractance and low-refractance layers are provided
between the high-refractance and low-refractance layers, thereby
increasing the abrasion-resistance of the lamination.
A heat wave shielding lamination constituted thus in accordance
with this invention is able to provide sufficient
abrasion-resistance without the need of any high-temperature heat
treatment and can be practically utilized for the windows of
automobiles or of buildings, spectacle lenses, plastic substrates
and other such purposes.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory view of the preferred embodiment of the
heat wave shielding lamination according to this invention.
FIG. 2 is a graph showing spectral characteristics of the heat wave
shielding lamination of FIG. 1.
FIG. 3 is an explanatory view for the purpose of comparing
constructions.
FIG. 4 is a graph showing spectral characteristics of the heat wave
shielding lamination of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In a heat wave shielding lamination according to the present
invention there are provided a visible light transparent substrate,
and on the heat source side thereof, an overlying composite
lamination consisting of at least two layers of visible light
transparent substance of a low refractive index and at least two
layers of visible light transparent substance of a high refractive
index alternately lying on each other, with the topmost layer being
a low-refractance layer.
In the embodiment of this invention the visible light transparent
substrate is formed of glass, plastic or the like. Each
high-refractance film is formed of a material selected from
TiO.sub.2, CeO.sub.2, ZnS, CdS and ZrO.sub.2 and is thick enough to
reflect infrared rays. Each low-refractance film is formed of a
material selected from SiO.sub.2, MgF.sub.2, LiF, CeF.sub.3 or
CaF.sub.2 and is thick enough to reflect infrared rays. It is
preferable that the topmost layer of a heat wave shielding
lamination be the low-refractance film selected from SiO.sub.2,
MgF.sub.2, LiF, CeF.sub.3 and CaF.sub.2 and is thick enough to
prevent reflection of visible light.
A heat wave shielding lamination thus constituted in accordance
with this invention exhibits excellent visible light transparency
and heat wave reflection characteristics, and is characterized by
the provision of a thin layer of Al.sub.2 O.sub.3 along the
interface between the high-refractance films and the
low-refractance films.
This invention provides a heat wave shielding lamination with a
greatly improved abrasion-resistance and hardly any degradation in
its visible light transparency or heat wave reflection
characteristics.
Also, because in this invention the above-mentioned optical
characteristics and abrasion-resistance can be obtained with films
formed on the surface of the substrate at an appropriate
temperature that is not higher than 200.degree. C., the lamination
can be easily formed on the windows of automobiles or of buildings,
or on the lenses of spectacles and cameras and on plastic and other
substrates which formerly involved problems because of the need for
high-temperature heat treatment.
Also, by providing at the interface between the low refractance
film and the high refractance film an interfacial layer of a
refractance more or less midway between said low and high
refractances, there is an easing of visible light interferential
reflection arising in each layer of the lamination, providing
improved visible light transparency and greater brightness.
EXAMPLES
FIG. 1 shows an embodiment of the heat wave shielding lamination
according to the present invention. As shown, the lamination
consists of TiO.sub.2 high refractance film layers 20, 22 and a
SiO.sub.2 low refractance film layer 40, these layers being
overlayed alternately on the heat source side of a substrate 10
which is an automobile window pane 5 mm in thickness with a
refractive index of 1.50 and which is transparent to light in the
visible and infrared zones of the spectrum. The topmost layer is a
SiO.sub.2 low refractance film 50 formed as an interferential
reflection prevention layer.
The interfacial layers 30, 32, 34 are provided at the interface
between the high refractance films 20, 22 and the low refractance
films 40, 50. The heat wave shield of this embodiment therefore
consists of a 7-layer lamination, these being the high refractance
films 20, 22, the low refractance films 40, 50 and the interfacial
layers 30, 32, 34 disposed therebetween.
In order that the thus-formed heat wave shielding lamination
satisfies the JIS abrasion-resistance requirements stipulated for
window glass of automobiles without degradation of the optical
characteristics, i.e. transparency to visible light and heat wave
reflectance, it is necessary to decide the thickness of each of the
films 20, 22, 30, 32, 34, 40, 50 and the material of the
interfacial layers 30, 32, 34 on the basis of the following
considerations.
Specifically, it is necessary to decide the optimum thickness of
the TiO.sub.2 high refractance films 20, 22 and the low refractance
films 40, 50 and that of the SiO.sub.2 film, on the basis of the
refractive index of the substance from which the film interlayers
30, 32, 34 are formed, and the thickness thereof, with the aim of
preventing degradation of the optical characteristics accompanying
the presence of said interlayers.
In addition, the material selected for use as the interfacial
layers 30, 32, 34 and the thickness of these layers must be such as
to conform to the JIS abrasion-resistance standard laid down for
glass for use in automobiles. In this invention, in order to
satisfy such requirements the interfacial layers 30, 32, 34 are
formed of Al.sub.2 O.sub.3. Computer simulation techniques were
used to decide the following thickness of each of the films 20, 30,
40, 32, 22, 34, 50 forming the lamination, taking into account the
measured refractive indexes of the TiO.sub.2, SiO.sub.2 and
Al.sub.2 O.sub.3 films and the wavelength (.lambda.=1,000 nm) at
the center of the infrared spectrum at which interferential
reflection occurs.
The thickness of the TiO.sub.2 high-refractance films 20, 22 was
set at 101.+-.5 nm, that of the SiO.sub.2 low-refractance film 40
was set at 155.+-.8 nm and that of the topmost SiO.sub.2
low-refractance film 50 at 82.+-.4 nm. The thickness of the
Al.sub.2 O.sub.3 interfacial layers 30, 32, 34 formed at the
interface between the TiO.sub.2 and SiO.sub.2 films was set at
10.+-.0.5 nm.
RF sputtering was used as follows to form the heat wave shielding
lamination of this embodiment. The substrate 10 is cleaned
ultrasonically with an organic solvent such as isopropyl and this
is followed by the use of RF sputtering in a vacuum chamber to
thoroughly remove any surface spots or stains. The high-refractance
films 20, 22, the low-refractance films 40, 50 and the interfacial
films 30, 32, 34 are then laminated on the surface of the substrate
one after the other, in the order 20, 30, 40, 32, 22, 34, 50. More
specifically, the TiO.sub.2 high-refractance film 20 was formed by
the RF sputtering of a TiO.sub.2 target in an argon atmosphere
containing 5% oxygen and having an overall pressure of
2.0.times.10.sup.-2 Torr, without any special heating of the
substrate.
This was followed by the formation of the Al.sub.2 O.sub.3
interfacial layer, using an Al.sub.2 O.sub.3 target and performed
under the same formation conditions used to form the
high-refractance film 20 and without even breaking the vacuum. This
was then followed by the formation of the SiO.sub.2 low-refractance
film 40, using an SiO.sub.2 target and the same formation
conditions and vacuum employed for the TiO .sub.2 and Al.sub.2
O.sub.3 films. By repeating this RF sputtering formation process
the heat-source side of the substrate 10 was overlaid by the
TiO.sub.2 high-refractance films 20, 22, the Al.sub.2 O.sub.3
interfacial layers 30, 32, 34 and the SiO.sub.2 low-refractance
films 40, 50, providing a 7-layer TiO.sub.2 /Al.sub.2 O.sub.3
/SiO.sub.2 lamination without any special heating of the
substrate.
As the heat wave shielding lamination of this invention does not
require high-temperature heat treatment, it is possible to apply it
practically in a wide range of fields in which such utilization was
formerly not possible because of the high-temperature heat
treatment which was involved.
The spectral transmittance characteristics of a heat wave shielding
lamination formed according to this embodiment are shown in FIG. 2,
which shows clearly that the heat wave shielding lamination of this
embodiment has good transmittance for visible light.
The lamination of this embodiment was next subjected to the
abrasion test used for glass for use in the windows of automobiles.
The Taber abrasion test method was employed for this purpose, and a
haze meter used to assess the resistance to abrasion. A Teledyne
Taber Abraser was used to perform the test in accordance with the
JIS standard conditions (Abraser CS-10F; load of 1 kg; 1,000
abrasions). Measurement with the haze meter following the test
showed a haze value of 1.9% for the heat wave shielding lamination
of this embodiment. The glass substrate was also subjected to the
Taber test under the same conditions and showed a haze value of
1%.
The possible reason for this improvement in anti-abrasion
properties is that the Taber test stipulated by JIS can be
considered as being a form of scratch test, in which case it
follows that there is a correlation between the hardness of the
load-bearing layer and its anti-abrasion properties. It is well
known that Al.sub.2 O.sub.3, with a Mohs' hardness of 9, is much
harder than TiO.sub.2, which has a Mohs' hardness of 6, or
SiO.sub.2, which has a Mohs' hardness of 7. This means that while
TiO.sub.2 and SiO.sub.2 are both considered as normally strong
enough to withstand ordinary abrasion, by interposing therebetween
Al.sub.2 O.sub.3, which is harder than TiO.sub.2 and SiO.sub.2, the
load is supported by this hard Al.sub.2 O.sub.3 layer, providing
the overall lamination with greater resistance to abrasion.
This being the case, it can be considered that if instead of
interposing Al.sub.2 O.sub.3 layers at all the interfaces, as shown
by 30, 32, 34 in FIG. 2 of this embodiment, the layers 32, 34 were
to be omitted and just the Al.sub.2 O.sub.3 layer 34 interposed to
support the load directly, a similar improvement in the
anti-abrasion properties of the TiO.sub.2 /SiO.sub.2 lamination
should be obtained. In fact, it was confirmed that providing the
lamination with just the Al.sub.2 O.sub.3 layer 34 resulted in
anti-abrasion properties that were far better than those exhibited
by a TiO.sub.2 /SiO.sub.2 lamination.
In the JIS standard for window glass for automobiles it is
stipulated that the haze value as measured following the specified
Taber test shall not exceed 2%. Therefore the automobile glass
overlaid with the heat wave shielding lamination of this embodiment
fully meets the abrasion-resistance requirements laid down by JIS
so the lamination is utilizable as a heat wave shielding on
automobile window glass.
COMPARATIVE EXAMPLE
The characteristics of the heat wave shielding lamination according
to this invention will now be described in comparison with the
conventional heat wave shielding lamination. The 4-layer
conventional heat wave shielding lamination shown in FIG. 3
consists of the same TiO.sub.2 high-refractance films 20, 22 and
SiO.sub.2 low-refractance films 40, 50 as those of the embodiment
of FIG. 1 laminated on the heat-source side of the same glass
substrate 10. The method of forming the films 20, 40, 22, 50 is
also the same one as that of the embodiment of this invention, with
the thickness of the TiO.sub.2 high-refractance films 20, 22 set at
103.+-.5 nm and that of the SiO.sub.2 low-refractance films 40, 50
set at 172.+-.8 nm and 86.+-.4 nm, respectively.
FIG. 4 shows one of the spectral characteristics of the lamination
of FIG. 3, specifically, its transmittance relative to wavelength.
From FIG. 4 it can be seen that these transmittance characteristics
are almost identical with those of the lamination of the present
invention as shown in FIG. 2. Thus, even though in this invention
an interfacial layer is provided between the high-refractance and
low-refractance films, there is no degradation in the spectral
characteristics of the lamination of this embodiment, said spectral
characteristics being substantially the same as those of the
conventional heat wave shielding lamination.
The conventional heat wave shielding of FIG. 3 was subjected to the
same JIS abrasion test conditions as the lamination of this
embodiment. This resulted in a haze value of 3.5% for the
conventional lamination, confirming that it did not possess the
requisite resistance to abrasion specified by JIS for the window
glass of automobiles. The heat wave shielding lamination according
to this invention, on the other hand, has far better abrasion
resistance than the conventional lamination while maintaining
almost identical spectral characteristics, fully confirming its
practical utility for the window glass of automobiles.
As described in the foregoing, the heat wave shielding lamination
according to this invention fully confirms to the JIS standard
relating to the abrasion-resistance of automobile window glass
without any degradation in spectral characteristics, specifically
the transparency to visible light and heat wave shielding
characteristics.
Compared with the above-described conventional heat wave shielding
lamination the lamination of this embodiment has more layers
because of the provision of the Al.sub.2 O.sub.3 at the interface
between the TiO.sub.2 and the SiO.sub.2 layers, and it might be
thought that this could have an adverse effect on the productivity
rate thereof. However, because the Al.sub.2 O.sub.3 is so extremely
thin the time needed for its formation is negligible compared with
the time required for the formation of the TiO.sub.2 and SiO.sub.2
layers, and as such there would be hardly any effect on the
productivity rate.
Furthermore, because the lamination according to this invention can
be formed without any heat treatment of the substrate at high
temperatures in excess of 200.degree. C., the lamination can be
formed on plastic and other such substrates which cannot be
subjected to high-temperature heat treatment. Moreover, the
excellent abrasion-resistance of the lamination of this invention
can be assumed to derive from the delicate interface structure
between the high-refractance and low-refractance layers, and not in
the kind of diffusion zones produced between high-refractance and
low-refractance films which have been subjected to high-temperature
heat treatment. Because of this, the lamination of this invention
is applicable not only to the windows of automobiles and buildings
but to many other product areas, such as scratch-prevention
coatings for spectacle and camera lenses, anti-glare coatings, and
the like; and when it has been provided with greater strength and
improved spectral characteristics, the lamination of this invention
will have an extremely wide range of applicability.
Also, because the abrasion-resistance of the heatwave shielding
lamination of this invention resides in the delicate structure of
the interface between the high-refractance film layers and the
low-refractance film layers, not in the mutual diffusion zones of
the interface, ordinary vacuum deposition, ion plating, sputtering,
chemical vapor deposition, cluster ion beam and other such
manufacturing methods can be used in addition to the
above-mentioned RF sputtering.
As will be clear from the above description, the present invention
relates to a heatwave shielding lamination which is provided with
sufficient optical characteristics and ample resistance to abrasion
without resort to special high-temperature heat treatment by the
formation of a prescribed interfacial layer at the interface
between the high-refractance layers and the low-refractance layers.
It is feasible therefore that the lamination thus constituted may
be utilized practicably for a wide range of purposes.
* * * * *